Field of the Invention
The present invention relates to a wear-resistant flexible circuit body suitable for movable units such as industrial robots and service robots, and relates to a method for production thereof.
Description of Related Art
In recent years, development of robots is remarkable, and robots capable of performing a variety of motions are appearing. In addition, with respect to wearable electronic equipment which can be fitted or attached to a human body or clothing, many varieties of such equipment are developed. Many electric wires for supplying electric power or for transmitting signals are used in these robots and wearable electronic equipment, but in general, an electric wire is constructed such that it has a copper wire as a core, with its outer periphery covered by an insulating material, so the electric wire itself has almost no elasticity. For this reason, it is necessary to arrange an electric wire while providing a margin so as not to obstruct the motion of a robot or a human body, which becomes an obstacle to the design of devices or practical use in many cases.
In particular, in equipment such as a front line humanoid type robot, a power assisted device which is worn or fitted on a human body so as to assist muscular power, many electric wires for operating end motors by way of multiple degree of freedom joints, respectively, and many electric wires for transmitting signals from various kinds of sensors arranged at end points are wired, and in order to enhance the degree of freedom of such wiring in the multiple degree of freedom joints, the demand with respect to those electric wires which are constructed to be elastic or expandable and contractable is increasing more and more.
On the other hand, in recent years, many arm robots are used as industrial robots. In this kind of arm robots, it is required that electrical cables for supplying electric power or for transmitting signals used for an end effector mounted on a tip side of a robot arm, a joint part of a robot arm, etc., be arranged to extend from a root side of a robot arm to a tip side thereof. In addition, depending on the drive form of the end effector or the joint part of the robot arm, it may be necessary to arrange an air (pneumatic) hose or a hydraulic pressure hose from the root side of the robot arm to the tip side thereof.
Accordingly, with the conventional arm robot, in cases where various kinds of cables such as an electrical cable, an air hose, a hydraulic hose, etc., are arranged in a joint part, in order to prevent bending or breaking (disconnection) of the cables, an extra length part is provided. In the extra length part, there is adopted a wiring technique in which the cables are once taken out to the outside in a base end side position of the joint part of the robot arm so that the cables are arranged in an outside space of the joint part, and then the cables are again introduced into the arm in a position which is nearer to its tip end than the joint part. In addition, there has also been known a construction in which a support rod is arranged at the position of the center of joint rotation in the joint part of the arm robot, and the support rod around which a cable has been wound in advance is received inside the robot arm so as to prevent bending or breaking (disconnection) of the cable (see, for example, the first patent document).
However, in the technique of arranging a cable in an outside space of a robot arm, a space for slacking the cable is required in the surrounding of the joint part of the robot arm. Further, there is a fear that at the time of the rotary operation of the joint part of the robot arm, the cable may be damaged and disconnected by being subject to an excessive force or interfering with the robot arm. In addition, in cases where the support rod is arranged in the position of the center of joint rotation, as disclosed in the first patent document, there are the following problems. In other words, the demand for expandable and contractible cables that make it possible to solve such a problem has also increased in the field of arm robots.
A flexible wiring board shaped in a zigzag or coil shape has been suggested to meet such a demand relating to the cables configured to be expandable and contractible. By using such a flexible wiring board, it is possible to increase the degree of freedom in wiring, without unnecessarily increasing the wiring length. Further, in the above-described robot arm, the cable can be prevented from damage and disconnection, without the necessity to provide a space for loosening the cable.    First Patent Document: Japanese patent application laid-open No. H8-57792    Second Patent Document: Japanese patent application laid-open No. H3-220787
However, the following problems are associated with the conventional flexible wiring boards. In the convention flexible wiring boards, a wiring layer is formed on the insulating film serving as a base layer, and an insulating layer is coated on the wiring layer. However, although an expandable and contractible flexible wiring board can be obtained by shaping into a zigzag shape, when the flexible wiring board catches on the surrounding components or rubs thereagainst, the wiring layer can be peeled off and disconnected and the flexible wiring board itself can be damaged.
Further, for example, when the flexible wiring board is used for a joint of a robot arm, the wiring layer can be disconnected and peeled off or the flexible wiring board itself can be damaged by large external forces, such as impacts and vibrations, acting upon the flexible wiring board.
Further, in addition to the flexible wiring board formed into a zigzag shape, a method for obtaining an expandable-contractible wave-shaped flexible circuit body is also known by which, for example, a band-shaped non-vulcanized rubber substrate is superimposed on the front and rear surfaces of a band-shaped wiring conductor in which slit copper foils or copper twisted wires are arranged in parallel, thereby shaping a flat circuit board, and the flat circuit board is then processed into the wavy shape in the lamination direction thereof (see, for example, the second patent document). In this case, the substrate should be bent a plurality of times at the production stage. The resultant problem is that the bending processing greatly reduces the adhesion between the laminated layers in the flexible circuit body. As a consequence, the above-described disconnection and peeling of the wiring conductor can occur and the flexible circuit body itself can be damaged. Further, since the vulcanized rubber substrate is heated and pressurized for simultaneous lamination on the flat conductor and shaping, although the zigzag shape can be obtained, a complex shape such as a coil shape is difficult to form.
Thus, in the conventional flexible wiring board, the wiring layer is disconnected and peeled off, or the flexible wiring board itself is damaged when the flexible wiring board comes into contact with the surrounding components or is subjected to a large external force such as impacts and vibrations. As a result, the connection reliability of the flexible wiring board can be lost and the service life of the flexible wiring board is difficult to ensure.